The invention relates to improved striking implements for sports or utility applications used to strike an object. More particularly, the striking implements of the present invention utilize the properties of shape memory alloys (SMA) that exhibit a stress-induced phase change to achieve high levels of elastic, reversible strain without permanent deformation in order to store and release significant levels of energy.
In recent years, there has been a growing demand among consumers for opportunities to participate in a variety of sports, both as a means of recreation and to improve general health. At the same time, there have been several breakthroughs in technology, some of which have been applied to the implements used in sports, and in some utilitarian tools. For example, in the sports implement field, while early golf clubs had shafts made of wood or wood composite, and club heads made of steel, these have been superseded by modem golf clubs with carbon-fiber reinforced shafts and titanium alloy heads. Moreover, sports implements have also been modified for form, to the extent that form dictates function and to the extent allowed by sports regulatory bodies.
Despite the significant advances in technology applied to striking implements, be they sports implements or striking tools, there exists the need to increase the ability of striking implements to store and release significant levels of energy with less effort exerted by the user. Additionally, there yet exists a need for implements that are able to absorb forces generated by an impact, while also protecting the user, and in the case of sports implements providing a pleasing xe2x80x9cfeelxe2x80x9d. In particular, for example, it is well-known that tennis players sometimes develop xe2x80x9ctennis elbowxe2x80x9d as a result of forces transmitted from the tennis racquet to the elbow, when the racquet strikes a ball with high impact. The challenge for technology is to reduce the amount of force transmitted to the user, while maintaining a sufficient xe2x80x9cfeelxe2x80x9d so that the user is able to exercise control, obtain instantaneous feedback and derive pleasure from playing the game. Moreover, the technology should be such that the implement, whether a tool (hammer, axe, etc.), or sports implement (such as golf club, hockey stick, tennis racquet, and the like), should be lightweight and retain its utility while at the same time having enhanced energy transfer, user control, and reduced transmission of impact forces to the user.
The present invention relates to the use of reversible strain properties of shape memory alloys at the flex point of a sports or utility striking implement. The use of a shape memory alloy element at the flex point of a striking implement yields a device capable of storing and releasing significantly higher levels of energy from the implement to an object, relative to conventional constructions, thereby improving the implement""s efficiency to perform work. The present invention also makes use of the vibration dampening property of the shape memory alloy, by itself and in combination with other materials that have efficient vibration dampening characteristics.
Embodiments of the invention are described in more particularity below. In summary, the invention modifies the shaft of a striking implement so that it comprises at least two shaft portions, with a shape memory alloy element bridging a gap between the two shaft portions, such that the element is able to flex when the implement strikes an object. In certain embodiments, to prevent over flexure and permanent deformation of the shape memory alloy element, the shaft is equipped with a stop (that may be a part of the shaft) that limits the degree of deformation of the element when the implement strikes an object. In other embodiments, a stop mechanism is not needed. In general, the shape memory alloy element is coaxially aligned with the shaft sections, and is affixed to each of the shaft sections by a range of optional attachment mechanisms such as polymeric plugs, couplings, and tapering of shaft ends to grip or clamp onto the element.
The invention provides several advantages, primary among these is the improved transfer of impact force from the implement to the object with less effort, due to a lever effect created at the flex point within the shape memory alloy by the stress-induced phase transformation of the alloy at this point of flexure allowing for large strains with minimal applied stress. The advantage of vibration dampening is also possible due to the shape memory alloy""s hysteresis during unloading of stored energy as well as when surrounded by other materials having vibration dampening properties. Fixing the location of the flex point at a specific point along the shaft or implement with the shape memory alloy also provides more consistent performance of the device.